This invention relates generally to cargo-handling apparatuses and systems for shipboard or marine use and more particularly to derrick cranes of the so-called double-topping type for shipboard use.
Ever since cargo handling by means of a double-topping derrick crane was developed as disclosed in the specification of Japanese Pat. No. 91,483, issued May 20, 1931, various improvements and developments relating to this type of cargo-handling machine have been made in several countries. This type of machines, which have thus been developed from light-lift derrick machines to heavy-lift machines of the type which can be operated doubly for fore and aft hatches, are still being widely used as efficient cargo-handling machines for shipboard use.
This invention relates to a cargo-handling machine of the above mentioned double-topping type doubly operable for fore and aft hatches which has a derrick boom which can be swung around a ship side and operated over a continuous range of azimuth angle of 300 degrees without the necessity of dismantling the boom topping tackle.
In spite of the above mentioned development of cargo-handling machines ot the double-topping type, the booms of their derrick cranes are limited in the range of azimuth angle in which they can operate, as described hereinafter. This limited working range is of the order of 60 degrees on each side of the ship centerline or a total of 120 degrees on each of the forward and after sides of the derrick post. That is, there are so-called "dead angle" zones each of the order of 40 to 60 degrees at the two sides of the ship into which a conventional derrick boom cannot be swung. In a conventional double-topping derrick crane, furthermore, the boom cannot be swung through the so-called dead angle from either of the forward and after sides of the derrick post to the other, that is, around the ship side.
Because of these limitations in the operational azimuth range of the booms of conventional machines of the instant character, difficulties arise in loading large and long cargo units as described hereinafter. These difficulties give rise to problems in view of the recent trend toward the shipment of cargo units of ever increasing size, particularly length.